For the synthesis of polysilanes, the Wurtz coupling method of condensing dihalosilanes with the aid of alkali metals has been most widely used partially because the starting reactants are readily available compared with other methods. Since the Wurtz coupling reaction proceeds through a complex polymerization mechanism, strict control of reaction conditions is necessary to obtain high molecular weight polysilanes in a well reproducible manner.
For example, if moisture is inadvertently introduced into a reaction system of synthesizing polyorganosilanes from organodihalosilanes and alkali metals in accordance with this method, siloxane bonds can form in polysilane skeletons, resulting in cleavage of the .sigma.-conjugation characteristic of polysilanes or disturbing the structural control.
For the purpose of reducing the moisture content as low as possible, a reaction system for the synthesis of organopolysilanes must be carefully set up. A reactor must be fully dried and the air in the reactor must be purged with dry inert gas. An organic solvent must be dried over metallic sodium and distilled before alkali metal particles are dispersed therein. The particles of alkali metal, for example, metallic sodium must be prepared by cutting a metal mass into appropriate size in a dry atmosphere. Although such individual procedures are done with special care for moisture, there is still left the possibility of moisture entry into the reaction system between the procedures, for example, during admission metallic sodium fragments into the reactor because of probable contact with the ambient atmosphere. Then siloxane bonds can be eventually formed in polysilane skeletons.